5. Conclusions
The use of ground granulated blast furnace slag (GGBFS) and steel fibers for concrete mixes for railway sleepers has been investigated. The appropriate mix proportions, mechanical properties, and durability performance of these mixes were discussed in this study, and following conclusions can be drawn: 1) The mix proportions with partial replacement of Type III Portland cement by ground granulated blast furnace slag were evaluated and mixes with a 56% slag replacement level showed not only improved performance but also less CO2 emissions. 2) The use of 0.75% of steel fibers in a slag concrete mix results in enhanced static and impact flexural capacity and toughness as well as sufficient workability for concrete casting. 3) Using new mixes incorporating GGBFS and GGBFS with steel fibers, a total of ninety prestressed concrete sleepers were produced under the same production process used for conventional railway sleepers. Concrete with the new mixes exceeded the strength requirements of the Korean Railway Standard but the strengths were somewhat lower than the laboratory mix test results. This underlines the need for careful quality control of the concrete for producing prestressed concrete sleepers. 4) The durability performance of the concrete mixes for prestressed concrete sleepers was also evaluated in terms of chloride ion penetration, carbonation, freezing and thawing, and scaling resistance. The mix with GGBFS (partial replacement of Type III Portland cement by GGBFS) showed improved resistance to chloride ion penetration and freeze-thaw cycles compared to the conventional concrete mix currently used for railway sleepers. The mix with GGBFS was more vulnerable to carbonation, however the predicted depth of carbonation was less than the concrete cover after 50 years of service.
